Hackers who penetrated the business networks of U.S. energy and nuclear companies in recent weeks were working for the Russian government according to a report in a prominent newspaper.

The Washington Post reported late Saturday that anonymous U.S. government officials confirmed the hackers were working for the Russian government.

The officials told The Post the Russians’ motive is not clear because the operations of the affected companies were not disrupted.

One U.S. official, however, said he viewed the cyberattack as “a reconnaissance effort,” to figure out points of entry into the companies.

“That’s what all cyber bad guys do,” the official said.

The attacks on the business and administrative systems of the companies were confirmed last week when the U.S. Department of Energy said it was helping the firms defend against the intrusions.

The U.S. Department of Homeland Security and the FBI had alerted the energy companies in late June that unidentified hackers were targeting the nuclear, power and critical infrastructure sectors.

The agencies said that at no time was there any risk to public safety.

News of the Russian government hacking into U.S. energy and nuclear companies follows the information that Russia mounted a hacking campaign designed to interfere with the recent U.S. presidential election.